This invention relates to the art of polybenzoxazole (PBO) polymers.
Polybenzoxazoles are a class of polymers within the larger class of polybenzazoles. Polybenzazoles (PBZ) are generally classified as AB-polymers, containing a plurality of mer units depicted in formula 1(a), or AA/BB, containing a plurality of mer units which conform with formula 1(b) ##STR1## wherein: each Ar is an aromatic group,
DM is a divalent organic moiety which is stable and inert in acid under polymerization conditions, PA1 each Z is either --O--, --S-- or --NR--, wherein R is a hydrogen atom or an aromatic moiety which is stable under PBZ synthesis and processing conditions and does not interfere with the synthesis or later use of the polymer. PA1 (1) nitrogen atoms and Z moieties in an azole ring are bonded to the aromatic group in ortho position with respect to each other; and PA1 (2) if the mer unit contains two azole rings, one nitrogen atom and Z moiety may be in either cis-position or trans-position with respect to the other nitrogen atom and Z moiety, as described and illustrated in 11 Ency. Poly. Sci. & Eng., supra, at 602, which is incorporated herein by reference.) PA1 (a) an aromatic group; PA1 (b) two o-amino-hydroxy moieties bonded to the aromatic group; and PA1 (c) a methyl group bonded to the aromatic group. PA1 (a) a first aromatic group; PA1 (b) two oxazole rings fused with the first aromatic group; PA1 (c) a methyl group bonded to the first aromatic group; and PA1 (d) a divalent organic moiety which is stable and inert under polybenzoxazole polymerizing conditions bonded to one of the azole rings.
(For the purpose of this application, when the nitrogen atoms and Z moieties of a mer unit are depicted as bonded to an aromatic group without indicating their position, as Formula 1(a)-(b), it shall be understood that:
In polybenzoxazole polymers, each Z group is an oxygen atom.
Polybenzazoles are synthesized by the reaction of one or more difunctional monomers, each of which contains at least two functional moieties chosen from the group consisting of electron-deficient carbon groups and o-amino-basic moieties. Such reactions are illustrated in formulae 2(a) and (b). ##STR2## wherein each Q is an electron-deficient carbon group and all other moieties have the meaning and preferred embodiments previously given. The divalent organic moiety DM ordinarily comprises an aromatic group.
Polybenzazole polymers, their properties and their synthesis are discussed in detail in the following references: Sybert et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,772,678 (Sep. 20, 1988); Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987); Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985); Wolfe et al., Liquid Crystalline Poly(2.6-Benzothiazole) Compositions, Process and Products, U.S. Pat. No. 4,533,724 (Aug. 6, 1985); Wolfe, Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6, 1985); Imai et al. "Polybenzoxazoles and Polybenzothiazoles," 83 Makromol. Chem. 167 (1965), Evers, Thermoxadatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymers, U.S. Pat. No. 4,359,567 (Nov. 16, 1982); Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S. Pat. No. 4,578,432 (Mar. 25, 1986) and 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (J. Wiley & Sons 1988), which are incorporated herein by reference.
Polybenzazoles are soluble in strong acids. However, they are substantially unreactive, and do not provide reactive sites to permit modification of the polymer properties, such as cross-linking to decrease solubility in acids. What are needed are monomers and polybenzoxazole polymers or copolymers which provide reactive sites.